Method of mounting a compact circuit package to a heat sink or the like

ABSTRACT

A compact circuit package includes a housing providing a cavity for containing heat generating electrical components. A ceramic substrate is mounted to close the cavity. The package is adapted to be mounted in heat transferring relationship with a heat sink. The bottom surface of the compact circuit package is provided with a self-contained chamber containing a supply of grease. The chamber is defined by the package bottom surface and a bubble of plastic film which overlies the substrate and which is removable sealed to the package around the periphery of the substrate. In this form, the compact circuit package can be transported and stored until ready for use. When the package is ready to be mounted to a heat sink, pressure such as by a finger is applied to the top surface of the bubble film to thereby spreadingly apply the grease to the surface of the substrate. The film is then removed from the bottom of the compact circuit package and the greasy underside of the film placed into engagement with the heat sink surface and rubbed, as by a finger, to thereby spread the remaining residue grease onto the heat sink. The film is then removed and discarded and the compact circuit package mounted to the heat sink.

This is a division of application Ser No. 546,999, filed Oct. 31, 1983,now U.S. Pat. No. 4,546,411.

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to the mounting of a compact circuit package to aheat sink or the like.

Heat conducting, electrically insulating substrates have beenadvantageously employed to retain heat generating electrical componentsalong a first substrate side while a second oppositely disposedsubstrate side may be mounted to a heat sink to permit the heatgenerated by the electrical components to pass through the electricallyinsulating substrate to be dissipated at the external heat sink. Onedesirable construction is shown in U.S. Pat. No. 3,958,075.

A wide variety of circuit constructions may be located at or near theinsulating substrate and within a cavity provided by the surroundinginsulated housing. By way of example, see U.S. Pat. Nos. 4,196,411 and4,218,724.

Referring more specifically to U.S. Pat. No. 4,218,724, heat conducting,electrically insulating substrates containing one or more heatgenerating electrical components have been advantageously connected toan insulating housing including a cavity surrounded by one or more edgesor abutments which engage the substrate to limit the extent of entry ofthe substrate into the cavity. Clamping pressure may be applied to theinsulating housing to clamp the substrate against an external heatdissipating object such as a heat sink to permit heat to pass from thesubstrate to the external heat sink without encountering any interveningthermal barriers such as solder, metalization, epoxy or the like.

The insulating housing is usually molded from a suitable plastic andprovided with an upper cavity portion which is closed by the substrateand which contains the heat generating electrical components. The bottomhousing portion is normally generally planular, surrounds the substrate,and is provided with relatively thin opposed outwardly extendingmounting flanges through which threaded bolts or the like extend tomount the assembly to a heat sink.

The electrically insulating substrate, which is usually made fromceramic sheet material is mounted to the housing bottom surface and maybe adapted to extend outwardly beyond the surface or may be flushtherewith.

It is highly desirable to provide for maximum heat transfer between theceramic substrate and the heat sink when the compact circuit package ismounted thereto. In order to fill the interstices in the substrate andheat sink surfaces, silicon grease has previously been manually appliedto these surfaces before mounting to thereby improve the heat transfercharacteristics. Such grease application was normally done in situ,wherein the circuit package installer dipped his fingers into acontainer of grease and spread the grease onto the ceramic substrate andheat sink with his fingers. This was not only messy, but also requiredthat the installer had a supply of grease readily at hand.

It is an object of the invention to provide an improved concept ofsupplying and applying grease to the interface between the substrate ofa compact circuit package and the heat sink to which the substrate isultimately mounted.

In accordance with the various aspects of the invention, the bottomsurface of the compact circuit package is provided with a self-containedchamber containing a supply of grease. The chamber is defined by thepackage bottom surface and a bubble of plastic film which overlies thesubstrate and which is removably sealed to the package around theperiphery of the substrate. In this form, the compact circuit packagecan be transported and stored until ready for use.

When the package is ready to be mounted to a heat sink, pressure such asby a finger is applied to the top surface of the bubble film to therebyspreadingly apply the grease to the surface of the substrate. The filmis then removed from the bottom of the compact circuit package and thegreasy underside of the film placed into engagement with the heat sinksurface and rubbed, as by a finger, to thereby spread the remainingresidue grease onto the heat sink. The film is then removed anddiscarded and the compact circuit package mounted to the heat sink.

The present invention addresses and solves the need for a single,effective technique for providing thermoconductive material at theinterface of the heat sink and the circuit package for enhancing heattransfer. Another solution is shown in my co-pending application Ser.No. 547,031, filed Oct. 31, 1983, now U.S. Pat. No. 4,546,410.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate the best mode presentlycontemplated by the inventor for carrying out the invention.

In the drawings:

FIG. 1 is a side elevation of a compact circuit package constructed inaccordance with certain aspects of the invention, with parts in section;

FIG. 2 is a bottom perspective view of the package and showing thebubble chamber;

FIG. 3 is a view similar to FIG. 2 and illustrating spreading of thegrease onto the package substrate;

FIG. 4 illustrates removal of the film from the package;

FIG. 5 is a perspective showing of the subsequent application of thegreasy side of the film to the heat sink and spreading of the remaininggrease thereonto; and

FIG. 6 is a side elevation of the compact circuit package mounted to aheat sink.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in the drawings, the concepts of the invention are directed toa compact circuit package 1 of the general type disclosed in the aboveidentified U.S. Pat. No. 4,218,724. Basically, package 1 includes anelectrically insulating housing 2 of molded thermoplastic or the like.Housing 2 includes a rectangular upper portion 3 defining an internalcavity 4 adapted to have a plurality of heat generating electricalcomponents 5 disposed therein. At least some of the components 5 may bemounted on a flat substrate 6 of any suitable material which serves toclose the open portion of cavity 4. The lower portion of housing 2includes a peripheral rim 7 which surrounds substrate 6, with the latterbeing mounted to housing 2 in any suitable well-known manner. In thepresent embodiment, substrate 6 is basically flush with rim 7, althoughthe substrate could protrude therebeneath. End flanges 8 extend from thebottom of housing 2 for purposes to be described.

The compact circuit package 1 is adapted to be ultimately mounted to anexternal heat dissipating object, such as the planular wall of a heatsink 9 or the like. See FIG. 6. In so mounting, it is desirable that themaximum interface heat transferring contact be made therebetween.

For this purpose, and referring to FIGS. 1 and 2, package 1 is providedwith an enclosed chamber 10 on its lower side. Chamber 10 is defined bythe exposed surface 11 of substrate 6 and rim 7, together with a thinbubble of plastic film 12 which overlies substrate 6. Film 12 may bemade of any suitable flexible plastic material such as various vinylbased thermoplastic resins developed and sold by Dow Chemical Co. Film12 is sealingly secured to package 1 around the periphery of substrate 6as by strips of adhesive 13 applied to rim 7. One end of film 12 extendsoutwardly beyond adhesive 13 to form a pull tab 14.

Chamber 10 confiningly contains a supply of heat transfer enhancinggrease 15 which in the present embodiment is shown as a plurality ofspaced deformable grease nodules 16. Grease 16 is preferably of thesilicon based type and may be applied in any suitable manner includingthe screening process.

The complete package assembly with its self-contained grease supply, asshown in FIGS. 1 and 2, may be manufactured at any desired location andstored for later use.

When package 1 is to be installed, it is taken to the site of heat sink9. The face 17 of heat sink 9 should be as flat, smooth and clean aspossible. Furthermore, it is preferable that heat sink 9 be made ofAluminum or Copper which has sufficient thermal mass to maintain thetemperature of substrate 6 relatively low, such as below 100° C.

Turning to FIG. 3, the grease 15 within chamber 10 is first caused tospread out into a layer, as at 18, onto exposed surface 11 of substrate6 within chamber 10. This is accomplished by pressing down on film 12 atnodules 16. Film 12 with a remaining residue 19 of grease thereon isthen removed from package 1 by pulling on pull tab 14 to peelinglyrelease the film from the peripheral adhesive 13, as shown in FIG. 4leaving layer 18 exposed. Referring to FIG. 5, film 12 is thenpositioned over face 17 of heat sink 9 so that the underside of the filmwith the grease residue 19 thereon is in contact therewith. Pressing andwiping of film 12 onto heat sink 9 causes the residue to be transferredto face 17 in a spreadout layer 20. Film 12 may then be removed anddiscarded.

FIG. 6 illustrates the final mounting of compact circuit package 1 toheat sink 9, as by bolts 21 passing through flanges 8 and threadinglyinto threaded openings 22 in the heat sink wall. The resultant assemblyprovides a final interposed grease layer 23 comprising a joinedcomposite of layers 18 and 20.

The invention provides a unique concept for increasing the thermaltransfer through grease at the interface between a compact circuitpackage and a heat sink. If desired, instructions for utilization of theinventive concept may be printed directly onto film 12.

Various modes of carrying out the invention are contemplated as beingwithin the scope of the following claims particularly pointing out anddistinctly claiming the subject matter which is regarded as theinvention.

I claim:
 1. A method of mounting a compact circuit package containingheat generating electrical components to the wall of a heat sink, andwherein said package includes a housing having a heat conductingsubstrate and with a bubble of film overlying said substrate andadhesively secured to said housing peripherally of said substrate andforming an enclosed grease containing chamber, said method comprisingthe steps of:(a) applying external pressure to the outer side of saidfilm to spread a layer of said grease onto said substrate within saidchamber, (b) removing said film from said housing so that said layer ofgrease on said substrate is exposed, (c) and securing said compactcircuit package to the wall of said heat sink so that said layer ofgrease is interposed therebetween.
 2. A method of mounting a compactcircuit package containing heat generating electrical components to thewall of a heat sink, and wherein said package includes a housing havinga heat conducting substrate and with a bubble of film overlying saidsubstrate and adhesively secured to said housing peripherally of saidsubstrate and forming an enclosed grease containing chamber, said methodcomprising the steps of:(a) applying external pressure to the outer sideof said film to spread a layer of said grease onto said substrate withinsaid chamber while leaving a residue of grease on the underside of saidfilm, (b) removing said film from said housing so that said layer ofgrease on said substrate is exposed, (c) wiping said film onto the wallof said heat sink so that said grease residue is transferred from theunderside of said film onto said heat sink to form a grease layerthereon, (d) and subsequently securing said compact circuit package tothe wall of said heat sink so that the grease from said layers ifdisposed therebetween whereby heat transfer from said package to saidheat sink is maximized.
 3. The method of claim 2:(a) wherein said greaseis initially contained within said enclosed chamber in the form ofspaced nodules, (b) and said external pressure is applied through saidfilm onto said nodules.
 4. The method of claim 3 wherein said filmremoving step comprises peeling said film from its peripheral adhesivesecurement to said housing.